A massive cyber attack from unknown sources that has been spamming bitcoin exchanges is highlighting some of the dangers people can encounter when they exchange cash for digital currencies like the bitcoin, experts said on Wednesday.

The attack, which is technically known as a distributed denial of service attack, involved thousands of phantom transactions, forcing at least three of the online platforms that store bitcoins and trade them for traditional currencies to halt withdrawals of bitcoins until they can determine which transactions were real.

It showed that bitcoin, which exists solely in cyberspace and operates on a software code written by an unknown programmer or group of programmers, is as vulnerable to such an assault as any other Internet-based business. It exposes the higher risks involved in owning and trading the instrument compared with the dollar and other traditional currencies. Bitcoins slumped in value as a result of the disruptions.

“Bitcoin is still an experimental protocol in its infancy,” said Micky Malka, a venture capitalist who is on the board of Bitcoin’s trade group, the Bitcoin Foundation.

“It will grow and mature over time,” he added. “No one should be investing an amount they cannot afford to lose.”

This week’s attack was not the first, said Andreas Antonopoulos, chief security officer for blockchain.info, a website that tracks bitcoin activity and provides online storage services for bitcoin users.

Antonopoulos is also a member of a group of core bitcoin programmers and is part of an emergency response team of programmers who have been working to fix the flaws in the code governing some bitcoin transactions that the attackers were exploiting. He said that work that should be completed by the middle of next week, echoing an estimate provided by a spokeswoman for the Bitcoin Foundation who said its core developers were all participating in the effort to fix the code.